Screens comprising a large number of backlit pixels have been known for some time and used in, for example, television sets, computers and portable devices of small size, such as, for example, mobile telephones, games consoles and calculators. The term “backlit” image zone connotes an image zone, which is situated in front of a light source which illuminates it from the rear. The image zone may for example be a pixel, a plurality of pixels or a part of a pixel (for example a liquid crystal pixel) or else a strip of film on which an image has been printed. In a backlit screen, a diffuse light source is placed behind the plane of the pixels, so as to improve the contrast.
Portable devices are generally powered by electric batteries, the duration between charges being a significant factor in convenience of use. With the aim of increasing this duration between charges, photocells have been integrated into these portable devices, which produce part of the current required for the operation of said device. Insofar as the space available for arranging photocells on the external surface of said portable devices is very restricted, it would be desirable to integrate the photocells into the display screen.
The prior art shows a certain number of examples of such integration. A first approach consists in depositing semitransparent photovoltaic cells (see EP 1 174 756 (ETA), U.S. Pat. No. 7,206,044 (Motorola), WO 2009/052326, US 2010/284055, WO 2009/065069 (Qualcomm), US 2010/245731 (Intel)). Another approach consists in depositing photovoltaic layers in the form of strips between which the light from the pixels passes (see US 2002/0119592 (BP), U.S. Pat. No. 4,795,500 (Sanyo), WO 2009/098459 (M-Solv)). All these approaches lead to screens which are either not very luminous, or the surface area of the photovoltaic cells, which is, for a given cell type, proportional to the energy converted, is small.
Document US 2007/0102035 (X. Yang) shows another approach to such integration, in which photocells covering zones arranged on the surface of the screen collect the ambient diffuse light, while a system of lenses arranged behind the display screen focuses the back-illuminating light onto zones that are not covered with photocells.
However, these photocells must not degrade either the imaging characteristics or the luminosity of the screen in which they have been integrated, and this is why the total area available for these photocells is in fact very restricted; indeed, the width of the photocells cannot be significantly greater than the space between two pixels, a space that it is desirable to minimize in order to improve the resolution of the screen. If the photocells are larger, and a fortiori when they partially cover the surface of the pixels, as is the case in the embodiment discussed above in document US 2007/0102035, the luminosity and the resolution of the image generated by the screen are degraded. This same document comprises another embodiment in which the back-illumination light is focused in the space between the photocells by a lens situated between the back-illumination light source and the substrate on which the array of pixels is located; this embodiment presents the drawback of requiring extremely precise positioning of the lens, both as regards its lateral position, but especially its distance with respect to the photocells. Moreover, it does not make it possible to integrate the light source for the backlighting directly into the substrate of the field effect transistors which control the liquid crystals forming the pixels of the screen.
The present disclosure therefore seeks to present a display screen with integrated photovoltaic cells, which allies a high proportion of photovoltaically active surface with a high luminosity of the display. Preferably, this integration of photovoltaic cells does not require substantial modifications to the design of the display screen, and in particular of the “pixel control” part, so as to be able to use known screen designs.
Within the framework of the present disclosure, this problem is solved by the judicious association of three essential elements: an array of pixels which generates an image, a plurality of photovoltaic cells, and a plurality of lenses forming a lenticular array. Each of these three elements is characterized by its shape, its dimension and its positioning with respect to the other, to form a digital display screen with integrated photovoltaic cells.